[Java] Remove Netty dependency from arrow-vector

[asfimport]

Cleanup remaining usage of Netty from arrow-vector and remove as a dependency after ARROW-9300.

Reporter: Bryan Cutler / @BryanCutler

Related issues:

• [Java] Remove Netty references from ArrowBuf and move Allocator out of vector package (is related to)
• [Java] Separate Netty Memory to its own module (depends upon)

_{Note: This issue was originally created as ARROW-9356. Please see the migration documentation for further details.}

[asfimport]

Wes McKinney / @wesm:
@BryanCutler @rymurr is this on your critical path for the next couple days?

[asfimport]

Bryan Cutler / @BryanCutler:
I took a quick look and don't think I could do this in the next couple of days. It's fine to push off until the next release.

[lidavidm]

It's now a test-only dependency (indirectly through arrow-memory-netty), other classes were vendored.